Whenever the color blue is invoked by poets and songwriters, they always seem to choose the sky or the sea as a metaphor. Poor Cherenkov Radiation never gets a look in. And yet, when observed, Cherenkov raditation is the most brilliant blue going. Sure, it’s a bit more of a mouthful than “the ocean” or “sky above”, but it’s definitely more exciting.

What is it? Well, picture a particle carrying an electric charge travelling through water, at a speed greater than light can move through that medium. Easy to imagine, of course. As the radiation passes through the water, it emits a light with a shorter wavelength than the usual wavelength. And, since there is more light with a short wavelength, the light appears blue.